Polarization Mode Dispersion Emulator Research Articles

Narrow- or wide-band channel for a high baud rate fiber communication system: a judgment based on a temporal and spectral evolution PMD model.

In optical fiber communication systems, the tendency to prefer increasingly higher baud rates, up to 100 or 200 Gbaud, compels us to deal with wideband fiber channels in which polarization effects must be treated in a more complicated manner. In contrast to the conventional 50 GHz bandwidth wavelength division multiplexing channel, polarization mode dispersion (PMD) is observed in an all-order manner in a wideband fiber channel beyond 100 GHz, rather than only first- and second-order. In this study, certain principles that should be followed in establishing a PMD emulation model in a wideband fiber channel were put forward. Then, a temporal and spectral evolution PMD model that can reflect and emulate the evolution features of the polarization effects in a real fiber channel was proposed and demonstrated. The analyses show the PMD model satisfies all the principles for the wideband channels. Finally, we suggested some approaches to define a narrowband or wideband channel only considering the polarization effects to deal with PMD in a high baud rate optical fiber communication system.

PMD Emulator based on PZTs attached to pieces of an Hi-Bi fiber

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

Controlled and compact first- and second-order polarization mode dispersion emulator

In this article, the development of a controllable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators, is presented. Using this device, the first- and second-order PMD is reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:765–769, 2015

A deeper analysis of the second order polarization mode dispersion in optical communications systems

This article presents a new approach to the combined analysis of the first and second-order polarization mode dispersion (SOPMD) and shows their importance in optical communication systems performance. How it affects the relation between second-order polarization mode dispersion (PMD) and the differential group delay (DGD) in a single mode fiber is discussed. The analysis is based on time or wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long term statistical characteristics of second-order PMD over a PMD emulator, and investigate the correlation between SOPMD, depolarization (DEP) and polarization dependent chromatic dispersion (PCD). Some authors calculate these modes from measurements obtained from the first order polarization mode dispersion, assuming a positive correlation between these effects, but this not the real relationship between them. A new interpretation of SOPMD was used to analyze the problem of the spectral stability in terms of the temperature. Actual techniques for determination SOPMD, consequently DEP and PCD, use the variation in time and/or wavelength. In some studies the results obtained for SOPMD are correlated to first-order PMD (FOPMD). This paper shows, based on measurements, that the correlation between first and second order Polarization Mode Dispersion (PMD) in the case where the last one is a function of the temperature can assume positive or negative values.

A new experimental approach to second-order polarization mode dispersion analysis for optical communications systems

This article analyzes the polarization mode dispersion (PMD) in optical fibers and presents a new approach for its measurement. This approach permits the combined analysis of the first-order PMD and the second-order polarization mode dispersion (SOPMD) in optical systems for different values of temperature. The relation between SOPMD and the differential group delay (DGD) in a single-mode fiber is discussed. The analysis is based on time/wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long-term statistical characteristics of SOPMD acquired by a PMD emulator constructed with some pieces of high birefringence fiber, and the correlation between the SOPMD, depolarization (Depol) and polarization-dependent chromatic dispersion (PCD) was investigated. A new interpretation of SOPMD is presented to analyze the problem of the temperature spectral stability. The actual techniques for SOPMD determination, consequently Depol and PCD, use the variation with time and/or wavelength. In some studies, the results obtained for SOPMD are correlated to first-order PMD. We demonstrate experimentally that the temperature is an important factor for the correlation between SOPMD and PMD and cannot be neglected in the optimization of high-speed optical communications links.

Polarization dependent loss complications on polarization mode dispersion emulation

Polarization dependent loss (PDL) and polarization mode dispersion (PMD) coexist in an optical network system. So, PMD emulation is normally complicated by PDL. In this paper, an analysis of the implications of PDL on PMD statistics is done using a 35-PMF section emulator. The first order PMD (FO-PMD) and second order PMD (SO-PMD) statistics of the emulator with a PDL value of 0.06dB approached the theoretical Maxwellian and Foschini et al. distributions respectively. On increasing the PDL value to 4.59dB, both FO-PMD and SO-PMD statistics were distorted away from the above theoretical distributions even with presence of high number of random mode coupling sites.

Dual-core photonic crystal fibers for tunable polarization mode dispersion compensation

A novel type of dual concentric core photonic crystal fiber (PCF) is proposed and theoretically analyzed, aiming at the design of tunable dispersive fiber elements for polarization-mode-dispersion (PMD) compensation. The adjustment of the fiber's geometrical birefringence through the proper selection of structural parameters leads to very high values of differential group-delay (DGD). Moreover, the value of DGD can be dynamically tuned by infiltrating the outer core capillaries of the PCF with an optical liquid, which allows for the thermal control of its refractive index. Such fibers are envisaged as tunable dispersive fiber elements for PMD compensation or emulation modules.

Demonstration of PMD compensation by using a DSP-Based OPMDC prototype in a 43-Gb/s RZ-DQPSK, 1200 km DWDM transmission

This paper reports the DSP-based prototype compensator we have made to compensate the polarization mode dispersion (PMD) in fibers . It was tested in one channel of a 40 × 43-Gb/s DWDM DQPSK system, which is the commercial product line, either in the back-to-back case by using a PMD emulator, or in a 1200-km transmission testbed. The prototype showed a good performance under the tests of fast SOP and PSP rotation, DGD jump variation, and moderate knock on the testbed in a period as long as 12 h.

Polarization mode dispersion emulation using polarization maintaining fibers: Fixed root-mean-square differential group delay but varying second-order polarization mode dispersion

We report on a polarization mode dispersion (PMD) emulator with a fixed root-mean-square differential group delay (RMS-DGD) but varying second-order PMD (SO-PMD) using only a combination of polarization maintaining fibers and a polarization controller. The SO-PMD control mechanism is not completely in real time. Besides controlling the mean PMD values of the emulator, simultaneous adjustments in the maximum and minimum values of PMD statistics can be performed. We therefore illustrate irregular fluctuations that occur around the RMS-DGD due to SO-PMD. This novel design can be used to further show the impact of a high first-order PMD segment on the DGD and SO-PMD statistical distributions that might occur in an optical network system.

Statistical PMD and PDL effects emulator based on polarization maintaining optical fiber segments

Low cost statistical PMD/PDL emulator is presented. The emulator was initially designed as a classical PMD emulator. But PDL measurements of the designed emulator show that it can be also used as statistical PDL emulator. The emulator was constructed by concatenating 15 highly birefringence optical fiber segments and randomly varying the mode coupling between them, by rotating the polarization state between them. The achieved numerical and experimental results show that the designed emulator can mimic the polarization effects (PMD and PDL) of a real modern optical fiber link.

Repeatable First-Order and Second-Order PMD Emulator Using Binary Polarization Switches

A repeatable first-order and second-order polarization-mode-dispersion (PMD) emulator using binary polarization switches is demonstrated. The rotation angles of polarization switches are plusmn22.5deg and are used in pairs between birefringent elements. Repeatability and stability are also verified in the design. Such a device can be potentially used as a compensator to provide tunable second-order PMD with the same amount of first-order PMD to further optimize the system performance.

PMD Effects in Fiber Optic Transmission Systems

Polarization mode dispersion (PMD) remains the most important limiting impairment for high bit rate transmission over optical fibers. In this article, after a brief description of PMD model and the associated statistic, we study the pulse distortion due to PMD using a powerful time-frequency diagram. This approach allows a very simple illustration of the second and high order PMD effects through effective pulse broadening. Finally, the PMD emulation issue and both electronic and optical compensation techniques are presented, that is a current field of cooperation between ENST-Bretagne and France Telecom R&D.

Emulation and Inversion of Polarization Mode Dispersion: A Lumped System and Pade Approximation Perspective

Polarization mode dispersion (PMD) has been a major impediment in achieving higher speeds in optical fiber communication systems. Various approaches and techniques for the basic theoretical analysis, modeling, simulation, and compensation of PMD have been proposed in the literature. In this paper, we present a novel and fresh approach to the modeling, emulation and inversion of PMD in optical fibers. In our approach, we first build a full PMD model based on coupled mode theory as a continuous-time, lumped and lossless system. We then develop systematic model dimension reduction techniques, adapted from Krylov-subspace based methods for large electronic systems, in order to obtain compact and low complexity PMD models. The reduced complexity models produced by our technique match the full PMD model over a specifiable frequency range of interest, have the same structure as the full model, and are amenable to efficient software and low complexity hardware implementations for emulation and inversion. Furthermore, the reduced compexity PMD modeling framework we develop in this paper can serve as a general formalism for studying the compressibility of PMD models and emulators.

Measurement of PMD tolerance in 40-Gb/s polarization-multiplexed RZ-DQPSK

We experimentally investigate the first-order polarization-mode dispersion (PMD) tolerance of two polarization-multiplexed (POLMUX) RZ-DQPSK signals at overall 40 Gb/s. The polarization demultiplexing is enabled by an automatic endless polarization stabilizer. Time-interleaving the two orthogonally polarized RZ-DQPSK signals minimizes the crosstalk due to the non-ideal polarization stabilization, while it represents the worstcase for the PMD-induced crosstalk. Bit-error rate measurements are performed both in back-to-back and after 25-km standard single-mode fiber. The PMD tolerance is evaluated as a function of the instantaneous differential group delay, introduced by a first-order PMD emulator. 40-Gb/s POLMUX RZ-DQPSK is more sensitive to PMD than single-polarization 20-Gb/s DQPSK, while it is more PMD-tolerant than 40-Gb/s NRZ-OOK. Besides, its chromatic dispersion robustness is similar to the single-polarization 20-Gb/s DQPSK. The combination of POLMUX and DQPSK is therefore very promising in view of transmission systems at high bit-rate.

Simple adaptive first‐order PMD compensator using a Faraday rotator and a variable DGD element

AbstractA two‐degree‐of‐freedom (DOF) polarization mode dispersion (PMD) compensator has been developed to cancel the effects of first‐order PMD. The compensator comprises of a Faraday rotator (FR) and a dynamically varying crystal differential‐group‐delay (DGD) element. Because of the reduced number of control parameters, the compensator potentially possesses the desirable features of simple control, fast response, and cost saving. Principle of operation is validated by theoretical analysis and successful automatic PMD compensation is achieved in a 40 Gbit/s nonreturn‐to‐zero (NRZ) system. The compensator increased the average DGD allowed from less than 23% per bit‐slot for the uncompensated case to 42% at an outage probability of 10−4. Fast response of the compensator is also observed. The optimum setting of the compensator can be found in about 10 nregulating steps for all PMD emulator (PMDE) setting. These features allow the effective mitigation of the first‐order PMD effects within an optical fiber channel. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2417–2420, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23669

Reducing the number of polarization controllers in all-fiber polarization-mode-dispersion emulators using polarization maintaining fiber sub-sections with unequal lengths

Using polarization-maintaining fiber (PMF) sub-sections with unequal lengths, an all-fiber polarization mode dispersion (PMD) emulator with reduced number of polarization controllers is proposed and demonstrated. With six polarization controllers and seven PMF sections, each consists of four sub-sections with unequal lengths and spliced at 45° relative to each other, the generated PMD first- and second-order statistical distributions are close to those of the real fiber link with negligible deviations, therefore, the cost of all-fiber PMD emulators, mainly from the electrically driven polarization controllers, is significantly reduced.

Statistics of Polarization-Mode Dispersion Emulators with Unequal Sections

We study two models for the generation of polarization-mode dispersion (PMD) with unequal, fixed-length sections: an isotropic model, in which the orientations of all the sectional PMD vectors are taken to be randomly and uniformly varying across the Poincare sphere, and a rotator model, in which all sections are taken to be linearly birefringent waveplates randomly rotatable with respect to one another. We describe the implementation of importance sampling for first- and second-order PMD in both models, including a targeting method for first-order PMD. We then use analytical and numerical methods to reconstruct the statistics of first- and second-order PMD for the two models. Our results show that the statistical properties of PMD depend significantly on the specific details of how PMD is generated.

Effect of second-order polarization mode dispersion on the performance of polarization mode dispersion emulators

We analyze the performance of multisection fiber polarization mode dispersion (PMD) emulators based on random fiber sectioning and ordered sectioning, with the inclusion of second-order PMD in individual sections. Numerical simulations show that this inclusion leads to (1) an asymmetry in the autocorrelation function (ACF) that increases with the magnitude of second-order PMD and whose form depends on the sign of the second-order term, and (2) a shift in the probability distribution functions of the differential group delay (DGD), and hence the mean DGD, with frequency that are undesirable. This behavior is found to be similar for both types of sectioning and has negligible effect on their corresponding background autocorrelation. This analysis leads to the requirement of suitable design parameters of fibers for which the second-order PMD in individual sections is minimized so that the desired ACF of the fabricated PMD emulator is symmetric and the mean DGD is the same at all frequencies.

Stable multiwavelength erbium-doped fiber laser at room temperature with tunable wavelength, wavelength spacing, and channel number

We experimentally studied a functional multiwavelength erbium-doped fiber EDF laser at room temperature incorporating a commercial highly nonlinear fiber HNLF and a comb filter based on a first-order polarization mode dispersion emulator PMDE. The tunability of the lasing wavelength, the wavelength spacing, and the number of channels were investigated. It is found that the tuning of the three pa- rameters can be achieved by changing the setting of the first-order PMDE and varying the pump current of the EDF amplifier. This feature is very important to make the fiber laser practicable in many applications.

Practical Solutions to Polarization-Mode-Dispersion Emulation and Compensation

Polarization-mode dispersion (PMD) still remains a challenge for high-data-rate optical-communication systems. Practical solutions are desirable for PMD emulation, monitoring, and compensation. The authors review and compare various techniques for PMD emulation and compensation, with an emphasis on the application of programmable differential-group-delay (DGD) elements for manipulating PMD effects. The authors pay special attention to advanced emulation techniques, such as importance sampling and the hinge model, for practical applications. The tunability of programmable DGD elements proves to be attractive for both system performance evaluation and overall optimization